Flexible Cathodes

ABSTRACT

This disclosure relates to methods of making a cathode for a lithium batter. The batterys include: (a) treating a cathode current collector with flame or corona; (b) coating a slurry containing iron disulfide, a first solvent, and a binder onto the cathode current collector obtained from step (a) to form a coated cathode current collector, in which the slurry contains about 73-75% by weight solids and the binder contains a polymer selected from the group consisting of linear di- and tri-block copolymers, linear tri-block copolymers cross-linked with melamine resin, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, tri-block fluorinated thermoplastics, hydrogenated nitrile rubbers, fluoro-ethylene-vinyl ether copolymers, thermoplastic polyurethanes, thermoplastic olefins, and polyvinylidene fluoride homopolymers; and (c) drying the coated cathode current collector obtained from step (b) to provide a cathode, in which the cathode contains no more than 0.5% by volume of the first solvent and is capable of being bent to 180°. This disclosure also relates to methods of making a lithium battery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. application Ser. No. 12/791,221, filed onJun. 1, 2010, which is a continuation of U.S. application Ser. No.12/408,869, filed on Mar. 23, 2009, now U.S. Pat. No. 7,753,968, whichis a continuation and claims the benefit of priority under 35 U.S.C.§120 to U.S. application Ser. No. 11/375,537, filed on Mar. 14, 2006,now U.S. Pat. No. 7,527,895, which is a continuation of and claims thebenefit of priority under 35 U.S.C. §120 of U.S. application Ser. No.10/290,832, filed on Nov. 8, 2002, now U.S. Pat. No. 7,033,698. Thecontents of all parent applications are hereby incorporated by referencein their entireties.

BACKGROUND

This invention relates to cathodes for lithium batteries.

Batteries are commonly used electrical energy sources. A batterycontains a negative electrode, typically called the anode, and apositive electrode, typically called the cathode. The anode contains anactive material that can be oxidized; the cathode contains or consumesan active material that can be reduced. The anode active material iscapable of reducing the cathode active material.

When a battery is used as an electrical energy source in a device,electrical contact is made to the anode and the cathode, allowingelectrons to flow through the device and permitting the respectiveoxidation and reduction reactions to occur to provide electrical power.An electrolyte in contact with the anode and the cathode contains ionsthat flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

The cathode of the battery can be prepared by applying a slurrycontaining an active material to a substrate, which can serve as thecurrent collector for the cathode. It is desirable to coat the substrateuniformly, because a uniform coating thickness can promote good batteryperformance. Certain extrusion processes offer good control of thecoating thickness, but cannot be used when the slurry contains materialsthat fibrillate, and thus become rigid, during the extrusion process.

SUMMARY

The invention relates to methods for making cathodes for lithiumbatteries, and to the cathodes produced by these methods. The batterysinclude forming a slurry containing active materials, a binder, and asolvent or solvents, coating a flexible current collector with theslurry, then drying and calendering the cathode.

The finished cathodes are very thin and very flexible. Single-sidedcathodes (i.e., cathodes in which only one side of the foil is coatedwith active materials) can be folded 180° to form pleats, or can bewound on small-diameter round or square mandrels, without any crackingor delamination of the coating. Double sided cathodes can be wound aswell, without cracking or delamination of the coating. The cathodes arecomparable in performance to cathodes made using stainless steel meshcurrent collectors. The thinness of the current collector allows for theuse of increased amounts of active material per volume.

In one aspect, the invention features a cathode for a lithium battery.The cathode includes: (a) a current collector including aluminum foil;and (b) active cathode material including: (i) manganese dioxide; (ii)conductive materials; and (iii) a binder selected from the groupconsisting of linear di- and tri-block polymers, linear tri-blockpolymers cross-linked with melamine resin, ethylene-propylenecopolymers, ethylene-propylene-diene terpolymers, tri-block fluorinatedthermoplastics, hydrogenated nitrile rubbers, fluoro-ethylene-vinylether copolymers, thermoplastic polyurethanes, thermoplastic olefins,and polyvinylidine fluoride homopolymers. The binder may be a tri-blockcopolymer, e.g., styrene-ethylene-butylene-styrene polymer.Alternatively, the binder may be EPDM rubber, a PVDF homopolymer, or alinear tri-block polymer cross-linked with a melamine resin, e.g.,styrene-ethylene-butylene-styrene cross-linked with a melamine resin.One or both sides of the current collector, which may consistessentially of aluminum, can be coated with active cathode material.

In another aspect, the invention features a flexible cathode for alithium battery. The cathode includes: (a) a current collector includingaluminum foil; and (b) active cathode material including: (i) manganesedioxide; (ii) conductive materials; and (iii) a binder.

In another aspect, the invention features a method for making a cathodefor a lithium battery. The battery includes: (a) combining a catalyst,conductive materials, a solvent, and a binder to form a mixture; (b)dispersing the mixture to form a slurry; (c) applying the slurry to asubstrate using a solution extrusion process to form a coated substrate;and (d) drying the coated substrate. The battery can further includecalendering the cathode after step (d).

The substrate can be an aluminum foil, which can be flame treated andcoated with a primer prior to step (c). The solvent can be a hydrocarbonsolvent, e.g., a paraffinic solvent or an aromatic hydrocarbon solvent.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a prismatic cell.

FIG. 2 is a scheme showing a coating process of the invention.

DETAILED DESCRIPTION

An electrochemical cell, such as the prismatic cell 10 shown in FIG. 1,includes an anode in electrical contact with a negative lead, a cathodein electrical contact with a positive lead, a separator, and anelectrolytic solution. The anode, cathode, separator, and theelectrolytic solution are contained within a case. The electrolyticsolution includes a solvent system and a salt that is at least partiallydissolved in the solvent system.

The cathode includes an active cathode material. The active material canbe, e.g., a metal oxide such as MnO₂. Electrolytic manganese dioxide(EMD) is preferred. Other active materials are described in Blasi etal., U.S. Ser. No. 10/022,289, filed Dec. 14, 2001, which is hereinincorporated by reference in its entirety. For example, the activematerial can be iron disulfide. The cathode also includes conductivematerials such as carbon black and graphite.

The cathode also includes a binder. It is desirable that the binder bemechanically, thermally, and chemically stable. Examples of binders thatcan be used include linear di- and tri-block polymers, preferably withno double bonds, or with conjugated double bonds, in the main polymerchain. The binder preferably includes 29 to 33% polystyrene. Otherexamples include linear tri-block polymers cross-linked with melamineresin; ethylene-propylene copolymers with an ethylene content of atleast about 40%; ethylene-propylene-diene terpolymers with ethylenecontents below about 70%; tri-block fluorinated thermoplastics (e.g.,TFE/HFP/VF2 terpolymer); hydrogenated nitrile rubber with at least about30% acrylonitrile; fluoro-ethylene-vinyl ether copolymers; thermoplasticpolyurethanes (TPU); thermoplastic olefins (TPO); and PVDF homopolymerswith molecular weights around 0.5M.

The binders may be modified to improve properties of the cathode. Forexample, cross linking or vulcanizing low molecular weight rubber canconsiderably improve the solvent resistance of the cathode. Actual crosslinking can take place in the dryer, during the coating process.

Block copolymers are preferred as binders. Specific examples includeKraton G 1651 (SEBS). Other desirable binders include Royalene 521(EPDM), Hylar 301 G (PVDF homopolymer) and Kraton G1901 (SEBS crosslinked with melamine resin).

Because binders other than polytetrafluoroethylene (PTFE) are used,fibrillation is not necessary to achieve a flexible cathode with goodcohesion. Furthermore, extrusion processes with relatively high shearrates can be used, because the risk of fibrillation-related thickness isminimized.

The active material, conductive materials, and binder are combined witha solvent or solvents to form a slurry. In formulating the slurry, theinteraction between the binder solution and the active powders (e.g.,the manganese dioxide, the carbon black, and the graphite) must beconsidered. The solvent determines the application rheology for thecoating process; solvents are selected to promote defect-free anduniform drying of the cathode. The solvents can also serve as a fugitiveplasticizers or latent solvents to control drying.

Preferred solvents include normal and branched hydrocarbons, such ashexane; iso- and cyclic paraffinic solvents such as VM&P Naphtha HT; andaromatic hydrocarbon solvents such as Shell Sol A100. Other hydrocarbonsolvents may be used as well. Blends of the solvents may be used aswell. For example, a blend may contain 40% by weight of an aromatichydrocarbon blend; 30% by weight of iso- and cyclic paraffins; and 30%by weight hexane.

A typical slurry formulation contains 1-10%, preferably 2-5%, by weightbinder, 50-80%, preferably 60 to 70%, by weight active powders, and25-40%, preferably 30 to 35%, by weight of solvent(s). On a dry basis,the cathode preferably contains less than about 3% binder by weight, andmore than about 97% of the active powders. The slurry solids arepreferably 65-75% by weight, and the viscosity range of the slurry isfrom 25,000 to 45,000 cps. Table 1 shows some typical cathodeformulations.

TABLE 1 Cathode slurry Dry cathode % w % v % w % v Binder 2.2 2.8 3.07.8 Powder mix 72.6 32.8 97.0 92.2 Solvent blend 25.2 64.4 0.0 0.0 Totalsolids 74.8 35.6 100.0 100.0

The cathode also contains a current collector. The current collector isgenerally an aluminum alloy, e.g., aluminum foil. The type of foil to beused will depend on the equipment used to coat the foil and wind theelectrodes. Examples of foils that can be used include alloy #1145,temper H19 at 1.0 mil (0.001 inch) thick, and temper H0 at 1.5 milthick. The foil can be flame-treated or corona-treated to improvewettability. Both methods can increase the surface energy of foil from35 Dyne/cm to 68-70 Dyne/cm. A primer can then be applied.Alternatively, foils with primers already applied can be purchased. Forexample, pre-primed foils can be purchased from Lamart Corp. A preferredcurrent collector is aluminum foil that has been primed with thecommercially available water-based primer (Acheson EB 012). The waterbased primer can be applied using spray, gravure, and intermittentreverse roll coating techniques. The coating weight is preferably 0.5 to1.0 mg/cm².

The first step in forming the cathode is to disperse the powders in thebinder solution. Slurry formulations can be dispersed using either aball mill or planetary mixer for bench scale processes (e.g., batch size0.75 kg), and a Henshel mixer FM 10 for scaled-up processes (e.g., batchsize 8 kg). The dispersion time can be between about 0.5 and 1.5 hours.The degree of dispersion is measured with a Hegman gauge. The slurrydensity is preferably about 1.8-1.9 g/cc; the slurry is preferably about73-75% by weight solids; the viscosity is preferably about 350-500 P at10 sec⁻¹ at 75° F. The viscosity is measured using a Brookfield DV III,50 rpm, spindle 7. The slurries made with these dispersion methods canbe stable for at least 5 days; some are still usable after eight weeks.

The next step in making the cathodes is to coat the aluminum foilcurrent collector with the slurry. This can be done using a closed,pressurized fluid dispensing system. Referring to FIG. 2, the slurry ispumped into pressure pot 30. Air 31 is pumped into the pot, forcing theslurry through slurry feed line 32. From the slurry feed line, theslurry enters metering pump 34. The metering pump regulates the flow ofsolution through feed line 36. Line 36 feeds into extrusion die 38. Foil40, which has been treated as described above, moves over backing roll42. As the foil passes by the extrusion die, the cathode slurry isapplied to the foil. The gap between the extrusion die and the backingroll determines the wet thickness of the coating. The current collectorcan be coated on one side, or on both sides. For example, the gapbetween the extrusion die and the backing roll can be set at 14-16 milfor the first pass of the foil. If the foil is 1 mil thick, this settingwill result in a coating on one side of the foil of about 7-10 mil, whendry. If the other side is to be coated, the gap between the backing rolland the extrusion die can be set to 23-25 mil. This will result in acurrent collector in which each side has a coating with a thickness ofabout 7-10 mil when dry. Since the foil has a thickness of about 1 mil,and each side has a layer of primer about 0.5 mil thick, the totalthickness of the dry cathode is 16-22 mil.

A lab coater with a 4-inch wide web can be used. The speed of thebacking roller can be set to yield a line speed of 19 cm/minute. Areverse comma coating technique can be used. The basis weight of the drycathode is optimally 45 to 50 mg/cm² per side. Solution extrusionmethods are further described in Modern Coating and Drying Technology(E. Cohen and E. Gutoff, eds., 1992) and Walter Michaeli, Extrusion Dies(2d rev. ed. 2000).

After coating, the cathode is dried by passing through zones in whichheated air is directed at the wet surface of the cathode. The air speedand temperature are gradually ramped from zone to zone. Exemplarytemperatures are 45-80° C. and 70-130° C. for zones 1 and 2,respectively. If the cathode is dried too quickly in the first zone, itcan be prone to cracking Exemplary coating and drying process parametersare shown in Table 2.

TABLE 2 Lab-scale process Pilot-scale process Coating techniqueExtrusion Reverse comma Line speed (mpm) 0.19 0.60 Dryer typeImpingement, 2 zone Impingement, 1 zone Dryer length (m) 2 × 1.2 1 × 4.5Dryer temperature T1 = 40-50° C. T = 80° C. T2 = 85-130° 0 Flow rate(cc/min) 1.9-2.2 Web width (mm) 89.0 152.5 Residual solvent <0.5% vol

Typically, bench-coated cathodes are considered to pass the drying testif the coating is uniform and defect-free after 15 seconds at roomtemperature and 3 minutes at 100° C. Analytical tests indicate that nomore than 0.5% of residual toluene is present in the dry cathode afterthis drying schedule.

After drying, the cathode is calendered. Before calendering, theuncoated edges of the cathode are slit off to avoid wrinkling of thecoating-free zones. The cathode can be calendered using a 4-rollmodified “Z” calender with a roll width of 12 inches and a roll diameterof 16 inches. The rolls may be heated or cooled as needed. The cathodeis preferably calendered off-line, in a continuous mode (e.g.,reel-to-reel). A 2×2 roll configuration with two nips, or a 2 rollconfiguration with one nip can be used. The materials are preferablycalendered between room temperature and 60° C. A line speed of 3feet/minute can be used.

The cathode is calendered to achieve a desired porosity. For example, insome embodiments, a porosity of 30-35% is desired. Other desiredfeatures for the calendered cathode include a total coating weight ofabout 100 mg/cm² for double-sided cathodes; a density of greater thanabout 2.85 g/cc; and an extension of no more than about 5%, andpreferably about 1.5% to about 2.5%. For cathodes coated on one sideonly, a green (i.e., dried but not calendered) cathode having athickness of 7-11 mil is preferably calendered to a total finishedthickness of about 6-8 mil (a coating layer of 4.5-6.5 mil, 1 mil thickfoil, and a 0.5 mil primer layer).

The finished cathode can be pleated. That is, it can be bent back onitself 180°, such that the two sides contact each other. A cathode thatconsists of a foil current collector coated on one side was folded withthe foil on the outside, and the coating on the inside. After beingpleated, the cathode showed no visible cracking.

The finished cathode can also be wound, that is, wound around a mandrel.A cathode consisting of an aluminum foil current collector coated onboth sides was wound around a 27.5 mm×0.9 mm mandrel. Visual inspectionrevealed that the coating was not cracked, even after the cathode waswound, although in some cases the foil may be cracked. Cathodes that canbe pleated or wound, as just described, are said to be “flexible.” Theadhesion of the coating can also be tested using a 10×10 square crosshatch test.

The cathodes can be used in lithium cells, such as the prismatic cell 10shown in FIG. 1. These cells also include an anode, a separator, anelectrolyte, and a container. The anode can consist of an active anodematerial, such as lithium. The separator can be formed of any of thestandard separator materials used in nonaqueous electrochemical cells.For example, the separator can be formed of polypropylene, (e.g.,nonwoven polypropylene or microporous polypropylene), polyethylene,and/or a polysulfone. Separators are further described in U.S. Pat. No.5,176,968.

The electrolyte can be in liquid, solid or gel (polymer) form. Theelectrolyte can contain an organic solvent such as propylene carbonate(PC), ethylene carbonate (EC), dimethoxyethane (DME), dioxolane (DO),tetrahydrofuran (THF), acetonitrile (CH₃CN), gamma-butyrolactone,diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methylcarbonate (EMC) dimethylsulfoxide (DMSO) methyl acetate (MA), methylformiate (MF), sulfolane or combinations thereof. The electrolyte canalternatively contain an inorganic solvent such as SO₂ or SOCl₂. Theelectrolyte also contains a lithium salt such as lithiumtrifluoromethanesulfonate (LiTFS) or lithium trifluoromethanesulfonimide(LiTFSI), or a combination thereof. Additional lithium salts, forexample, lithium iodide, that can be included are listed in U.S. Pat.No. 5,595,841, which is hereby incorporated by reference in itsentirety. In some embodiments, the electrolyte may contain LiPF₆; inother embodiments, the electrolyte is essentially free of LiPF₆. Theelectrolyte also contains a perchlorate salt, which inhibits corrosionin the cell. Examples of suitable salts include lithium, barium,calcium, aluminum, sodium, potassium, magnesium, copper, zinc, ammonium,and tetrabutylammonium perchlorates. Generally, at least 500 ppm byweight of the perchlorate salt is used; this ensures that there isenough salt to suppress corrosion. In addition, less than about 20,000by weight of the perchlorate salt is generally used. If too muchperchlorate salt is used, the cell can be internally shorted undercertain conditions during use. The electrolyte is further described inBlasi et al., U.S. Ser. No. 10/022,289, filed Dec. 14, 2001.

To assemble the cell, a separator can be cut into pieces of a similarsize as the anode and the cathode and placed between the two. The anode,cathode, and separator are then placed within a case, which can be madeof a metal such as nickel, nickel plated steel, stainless steel, oraluminum, or a plastic such as polyvinyl chloride, polypropylene,polysulfone, ABS or a polyamide. The case is then filled with theelectrolytic solution and sealed. Additional methods for assembling thecell are described in U.S. Pat. Nos. 4,279,972; 4,401,735; and4,526,846. Other configurations of battery 10 can also be used,including, e.g., the coin cell configuration.

The invention is further described in the following examples, which donot limit the scope of the invention described in the claims.

Example 1

A cathode was prepared using the techniques described above. The slurryincluded:

styrenic block copolymer (Kraton G1651) 31.0 g active powder mull mix1000.0 g (EMD, carbon black, graphite) aromatic hydrocarbon solvent(Shell Sol A100) 140.8 g paraffinic solvent (VM&P Naphtha HT) 105.6 ghexane 105.6 g

The slurry was used to coat both primed and unprimed aluminum foil.Cathodes were prepared as described above, and their performance wasmeasured in two test vehicles (2/3A cell and coin cell). The performanceof the flexible cathodes was compared to cathodes made with stainlesssteel expanded mesh current collectors. In the 2/3A cells, theperformance of the cathodes was comparable. In the coin cells, theperformance for the flexible cathode made using primed foil wascomparable to that of the cathode with a stainless steel currentcollector, but the cathode made with unprimed aluminum foil had aperformance 30% below that of the cathode made with the stainless steelcurrent collector. The flexible cathodes could be wound around a 0.177inch mandrel without cracking and delamination and could be pleated.

Example 2

A cathode was prepared using the techniques described above. The slurrycontained:

Uncured EPDM rubber (Royalene 521) 31.0 g Active powder mull mix 1000.0g aromatic hydrocarbon solvent (Shell Sol A100) 194.5 g paraffinicsolvent (VM&P Naphtha HT) 194.5 g

The flexible cathodes could be wound around a 0.177 inch mandrel withoutcracking and delamination; the cathodes could also be pleated.

Example 3

A cathode was prepared using the techniques described above. The slurrycontained:

High molecular weight PVDF (Hylar 301F) 31.0 g Active powder mull mix(EMD, carbon black, graphite) 1000.0 g N-methyl pyro 519.0 g

The flexible cathode could be wound around a 0.177 inch mandrel withoutcracking and delamination.

Example 4

A cathode was prepared using the techniques described above. The slurrycontained:

Styrenic block copolymer (Kraton G1901) 31.0 g Active powder mull mix674.3 g Melamine formaldehyde resin (Cymel 303) 2.78 g Catalyst (Cycat)0.43 g Aromatic hydrocarbon solvent (Shell Sol A10) 55.4 g VM&P NaphthaHT 41.6 g Hexane 41.6 g

The flexible cathode could be wound around a 0.177 inch mandrel withoutcracking and delamination.

All publications, patents, and patent applications mentioned in thisapplication are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

Other Embodiments

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, although the examples described above relate to cathodes forprimary (i.e., non-rechargeable) lithium batteries, the invention can beused to prepare cathodes for rechargeable lithium batteries as well.Other embodiments are within the scope of the following claims.

1. A lithium battery comprising a housing and within the housing: (a) ananode comprising lithium; (b) a cathode comprising a cathode currentcollector and a uniform and defect free coating on the cathode currentcollector comprising iron disulfide, residual hydrocarbon and/orparaffinic solvent, and a binder selected from the group consisting oflinear di- and tri-block copolymers, linear tri-block copolymerscross-linked with melamine resin, ethylene-propylene copolymers,ethylene-propylene-diene terpolymers, tri-block fluorinatedthermoplastics, hydrogenated nitrile rubbers, fluoro-ethylene-vinylether copolymers, thermoplastic polyurethanes, thermoplastic olefins,and polyvinylidene fluoride homopolymers; (c) an electrolyte comprisingdimethyloxyethelene, dioxolane, and lithium iodide.
 2. The battery ofclaim 1, wherein the binder comprises a linear tri-block copolymer. 3.The battery of claim 2, wherein the binder comprises astyrene-ethylene-butylene-styrene polymer.
 4. The battery of claim 1,wherein the cathode current collector comprises aluminum or an aluminumalloy.
 5. The battery of claim 1, wherein the cathode current collectorcomprises an aluminum foil.
 6. The battery of claim 1, wherein thesolvent comprises a hydrocarbon solvent.
 7. The battery of claim 6,wherein the hydrocarbon solvent is an unbranched hydrocarbon.
 8. Thebattery of claim 6, wherein the hydrocarbon solvent is a branchedhydrocarbon.
 9. The battery of claim 6, wherein the hydrocarbon solventis an aromatic hydrocarbon.
 10. The battery of claim 1, wherein thesolvent comprises a paraffinic solvent.
 11. The battery of claim 10,wherein the paraffinic solvent is an iso-paraffinic solvent.
 12. Thebattery of claim 10, wherein the paraffinic solvent is acyclo-paraffinic solvent.
 13. The battery of claim 1, wherein thecathode has a thickness of from 16 mil to 22 mil.
 14. The battery ofclaim 1, wherein the cathode further comprises a conductive materialselected from the group consisting of carbon black and graphite.
 15. Thebattery of claim 1, wherein the cathode has a porosity of from 30% to35%.
 16. The battery of claim 1, wherein the cathode comprises less thanabout 3% by weight of the binder.
 17. The battery of claim 1, whereinthe cathode is capable of bending 180°.
 18. A method of using a primarylithium battery, the battery comprising a housing and within the housing(a) an anode comprising lithium (b) a cathode comprising a cathodecurrent collector and a uniform and defect free coating comprising irondisulfide and a binder selected from the group consisting of linear di-and tri-block copolymers, linear tri-block copolymers cross-linked withmelamine resin, ethylene-propylene copolymers, ethylene-propylene-dieneterpolymers, tri-block fluorinated thermoplastics, hydrogenated nitrilerubbers, fluoro-ethylene-vinyl ether copolymers, thermoplasticpolyurethanes, thermoplastic olefins, and polyvinylidene fluoridehomopolymers and (c) an electrolyte consisting of (i)dimethyloxyethylene, dioxolane and optionally other solvents, and (ii)lithium iodide and optionally other salts, the method comprisingdischarging the battery only once and then discarding the battery. 19.The method of claim 18, wherein the binder comprises astyrene-ethylene-butylene-styrene polymer.
 20. The battery of claim 18,wherein the cathode current collector comprises aluminum or an aluminumalloy.
 21. The battery of claim 18, wherein the cathode furthercomprises a conductive material selected from the group consisting ofcarbon black and graphite.
 22. The battery of claim 18, wherein thecathode has a porosity of from 30% to 35%.
 23. The battery of claim 18,wherein the cathode comprises less than about 3% by weight of thebinder.